This is a phase III, double-blind, placebo-controlled, multi-centered, dose-ranging, efficacy and safety study of tiludronate in post-menopausal women with low bone mass and no vertebral fracture. The study will include a minimum of 300 subjects randomized to either placebo, 50mg or 200 mg tiludronate orally once daily for the first seven days of each month of the two year treatment phase. Daily supplemental calcium will be used for the remainder of each month. Upon completion of the treatment phase, a one year observation phase will consist of daily calcium supplement for all subjects.